The control of semiconductor power components used in power electronics equipment generally requires a separation of potentials to insulate the control section from the power section. In conventional thyristors used as semiconductor power components, the potential separation is accomplished by means of a pulse transformer which feeds the control current directly to the gate-cathode path, i.e., the control path of the thyristor. In power transistors and thyristors which can be disconnected on the control current side, i.e., GTO thyristors, the cost for potential-separated control has risen sharply. In general, control currents in pulse form of both polarities are required, for instance, a positive pulse for switching on and a negative pulse for switching off the semiconductor power component. In addition, the control currents and voltages, respectively, must be present during the "on" and "off" times of the semiconductor power component, for instance, a positive control current during the "on" time and a negative control voltage during the "off" time.
Japanese patent No. A 57-12 62 70(A) discloses device in which one of the secondary windings of a first transformer is connected via rectifiers directly to the gate-cathode path of a GTO thyristor. The positive control current is fed-in during the "on" time via this first secondary winding. Via the second secondary winding, a capacitor is charged as an auxiliary voltage source which can be discharged via a transistor to the primary winding of a second transformer. The secondary winding of the second transformer is also connected to the gate-cathode path of the GTO thyristor for feeding-in, via diodes, a negative disconnect current. With this circuit arrangement, the current slope of the control currents is limited by the leakage inductances of both pulse transformers. This leads to difficulties especially in the case of stringent requirements as to the insulation voltage and in the control of high-power semiconductor components.
Another control unit for the potential-separated control of power transistors is known in which the control information, i.e., the command for switching a power transistor on or off with separated potentials, is transmitted by optoelectronic means. The control information drives a pulse amplifier which connects alternatingly two auxiliary voltage sources with opposite polarities to the gate-emitter path of a power transistor. The auxiliary voltage sources, which also supply power to the pulse amplifier, are likewise separated as to potential. Disadvantageously, this type of control unit is a very costly device.
Thus, the problem arises to develop a method and device for potential-separated control of semiconductor power components in such a manner that the cost for the potential-separated transmission of the control power as well as the control information is reduced.